1. Field of the Invention
The present invention generally relates to a method and system for manipulating video signal parameters and, more particularly, to a method and system that is especially useful for manipulating video signal parameters relating to video signals that have been recorded on videotape.
2. State of the Art
In modern video technology, it is commonplace to extensively adjust and modify video signal information on videotape for broadcasting and other teleproduction purposes. For example, videotape recorders are commonly used to electronically splice new video information onto videotape in the midst of existing information and to successively add video information at the end of other information. In such operations, the added video information may originate from other videotape recorders, from broadcast sources, or directly from live sources. Also, video signal information replayed from videotape recorders can be modified to provide special effects.
In video output signal information from videotape recorders, it is typical to encounter time displacement errors. While such errors can be introduced from various mechanical and electronic sources during recording and playback processes, there are four typical causes: tape-motion irregularities, head-motion irregularities, tape-dimension changes, and skew errors. These factors can cause variations in the mechanical scanning speed and in the linear speed of videotape through videotape recorders. Upon playback of videotape, time displacement errors can produce picture instabilities such as jitter and flutter and can cause wrong colors, lack of color, or unstable color in pictures.
To alleviate time-displacement errors in output signals from videotape recorders, it is well known to use time-base correctors. Generally speaking, time-base correctors correct time-displacement errors by synchronizing video output signals with stable timing signals to provide stable output signals. Many modern time-base correctors include analog-to-digital conversion circuits to digitize video signal information, integrated circuit memory elements to store the digitized signals, synchronizing circuitry to coordinate output signals from the time-base corrector with stable timing signals generated from independent (i.e., off-tape) sources, and digital-to-analog conversion circuitry to convert digital output signals to analog form for final output. One advantage often provided by time-base correctors is that the video signal information can remain stored in memory for extended periods without degradation and can be recovered by the synchronizing circuitry at selected times, and at controlled rates, in synchronization with stable timing signals that are generated independently of the videotape.
Time-base correctors are used in various systems to provide output signals that are stable, properly synchronized with signals from independent sources, and essentially free from phase differences or other timing displacement errors and irregularities. For example, modern time-base correctors are sometimes employed to manipulate output signals from videotape recorders of the helical scan type so that the manipulated output signals are satisfactory for broadcasting. Also, time-base correctors can be used to manipulate signal information from other sources, such as satellite transmissions, to overcome time displacement errors and to achieve other effects. Further, it is known in teleproduction systems to provide time-base correctors at the input to videotape recorder devices; in such systems, the timebase correctors condition or modify video signal information prior to transmittal of the information to the input of the recorders.
Modern time-base correctors, such as the ones included in advanced video processors sold under the trademark "Zeus" by Ampex Corporation of Redwood City, California, often include controls to manipulate and adjust various video signal parameters including ones which are not directly related to time-base errors. For example, time-base correctors may provide adjustments for video level, black level, chrominance level, chrominance phase, output synchronization to burst subcarrier phase, subcarrier phase, horizontal phase, input burst crossing select phase, horizontal blanking, vertical picture position, horizontal picture position, adaptive comb filter, and frame positioning. Some time-base correctors, including those used in broadcasting studios, may provide functions in addition to those mentioned above. Among the most common extra functions are dropout compensation, heterodyne operation, and system phasing controls. Manipulation and adjustment of such video signal parameters are made to enhance video picture quality and, in some situations, to add special effects to video images.
According to current practice, controls on time-base correctors to manipulate and adjust video signal parameters are directly linked to circuits for controlling the parameters. Thus, it is common for some video signal parameters to be manually adjusted by setting potentiometers on the time-base correctors or associated control panels.
It is also known in the teleproduction art to use editing devices to simultaneously control operation of several videotape recorders to, thereby, facilitate editing of videotapes. Through use of such editing devices, an operator of a teleproduction system can fairly easily produce, for example, edited videotapes having portions originating from several videotape recorders as well as outside signal sources. In such teleproduction systems employing several videotape recorders controlled by a single editing device, time-base correctors are usually separately associated with each of the videotape recorders. In such systems, the time-base correctors are usually controlled directly via the videotape recorders or through control panels associated with the videotape recorders. Thus, it is known to provide electronic communication between videotape recorders and time-base correctors, usually via serial data buses, for adjustment of operation of the time-base correctors.
In present practice, many of the controls and functions that are provided in time-base correctors are not used to their full potential. For example, in typical teleproduction systems, substantial delays often exist between the time that adjustments to video signals might be made and the time that adjustments are actually made, if at all, through control of time-base correctors. The fact that teleproduction system operators often delay or neglect adjustments that could enhance the output quality of video signal information is primarily a result of the fact that, in present teleproduction systems, adjustment of video signal parameters is often inconvenient, complex and frequently impractical to even attempt in "real time" (i.e., while a videotape is playing or while a video signal is being received). Further, because many of the controls for video signal parameters are of the analog type, manual adjustment of such controls is imprecise since exact levels cannot be repetitively set from machine to machine. Moreover, manual adjustment of time-base correctors may introduce operator error, particularly in teleproduction systems that include several videotape recorders which are to be operated simultaneously. Thus, operators of teleproduction systems often forgo, or delay, adjustments to video signal parameters to the detriment of video picture quality.
In light of conventional practice, it can be appreciated that a need exists for improvements in the manipulation of video signal parameters through the use of time-base correctors in complex videotape recording and playback systems. Specifically, there exists a need for methods and systems that assure that adjustments to time-base correctors can be conveniently and precisely implemented during replay of videotape from videotape recorders associated with the time-base correctors. Even more particularly, it may be seen that there exists a need for improvements in the control of video signal information parameters in systems wherein a single videotape editing device is used to schedule and control a plurality of videotape recorders and associated time-base correctors that often must operate simultaneously.